The present invention is related to a wind energy plant with a hydraulically actuated rotor brake.
Wind energy plants have generally a rotor brake in the drive train. The rotor brake is mostly arranged behind the gearbox, and in wind energy plants with an active pitch adjustment, it serves as an additional braking system, by which the rotor of the wind energy plant is maintained in its position when it stands still.
Erich Hau points out in Windkraftanlagen, 3th edition, Springer-Verlag Berlin, Chapter 8.7, the entire contents of which is incorporated herein by reference, that braking the rotor to stand still is unavoidable for maintenance and repair works, and is in general also usual during the normal standstill periods. With respect to the function of the rotor brake in the operation, it is further pointed out that the same is limited to the pure holding function at rotor standstill in the simplest case. It is said that the brake must be dimensioned for the required holding moment of the rotor at standstill in this case. In addition to its function as a pure holding brake, the rotor brake might in principle also be dimensioned as a service brake, provided that the braking moment and the braking power (thermal load) are sufficient.
In wind energy plants in which the rotor brake is a part of the safety system, the braking system is realised as a passive brake or as a so-called FailSafe-brake. This means that the brake has to be pressurised in order to reduce the braking moment bearing on or in order to release the brake completely. The braking moment of the passive brake is achieved by a spring assembly, which pretensions the assigned brake shoes into the braking position. The braking moment applied in doing so is generated by the elastic force exerted by the spring elements. Due to this, it is necessary to provide correspondingly great spring assemblies in the brake for a wind energy plant, which necessitates a strong braking moment. The passive rotor brake described above is released by introducing a hydraulic fluid into the brake cylinder, for instance. The hydraulic fluid is introduced into the brake cylinder such that its pressure acts against the force of the spring assembly.
In contrast to the passive brakes described above, active brakes for wind energy plants are also known, in which the braking moment is not applied via a spring assembly, but instead at increasing hydraulic pressure the braking moment gets also stronger. The advantage of an active brake is that the same can be made smaller and that it is significantly more cost-saving. Also, a significantly greater braking moment is possible with an active brake.
When using an active brake as a service brake, thus for braking down the rotating drive train, high pressure variations may occur due to tolerances in the run-out and in the thickness of the brake disc. High pressure variations occur in particular in the case when hydraulic fluid is tensioned in the brake cylinder and its supply line with the aid of a pressure reducing valve. Using a pressure reducing valve in the hydraulics is necessary for active brakes in particular, inasmuch as the same are used as service- or holding brakes.
The present invention is based on the objective to provide a hydraulically actuated apparatus which compensates pressure variations with simple means, which take place in the braking with a tensioned volume of hydraulic fluid.